We would like to use A/B testing in Journey Builder. I saw there was no such option out-of-the-box, but is there a workaround? When I say "A/B Testing", I don't mean just having a random split to monitor which of the 2 email versions has a better-performing e.g. subject line. Rather, we'd like a standard A/B functionality from Email Studio, whereby Marketing Cloud evaluates how each version of the e.g. subject line performed on the 20% list, and sends the "winning" version to the remainder of the list (80%) automatically.
Yes, the most simple way is to use a Random Split.
The downside of this is that you will have to figure out a way to create reporting, which won't be as easily displayed as the one in the A/B Test in Email Studio. As a workaround, you could include Engagement Splits in your journey, just before the Exit, to see how many subscribers engaged with each version of your email.